EP0517468B1

EP0517468B1 - Ink jet recording method and apparatus

Info

Publication number: EP0517468B1
Application number: EP19920305020
Authority: EP
Inventors: Hitoshi C/O Canon Kabushiki Kaisha Sugimoto; Hiromitsu C/O Canon Kabushiki Kaisha Hirabayashi; Shigeyasu C/O Canon Kabushiki Kaisha Nagoshi; Hiroshi C/O Canon Kabushiki Kaisha Tajika; Atsushi C/O Canon Kabushiki Kaisha Arai; Yuji C/O Canon Kabushiki Kaisha Akiyama; Miyuki C/O Canon Kabushiki Kaisha Matsubara
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 1991-06-03
Filing date: 1992-06-02
Publication date: 1996-10-16
Anticipated expiration: 2012-06-02
Also published as: DE69214520D1; ES2092641T3; DE69214520T2; JPH04355157A; JP2941998B2; EP0517468A3; EP0517468A2; US5477248A; ATE144199T1

Abstract

In an apparatus for recording color images making use of a plurality of inks of different colors (Y, M, C, K), the penetrability of at least one ink is caused to differ from that of the other inks. In particular, the penetrability of an ink higher in lightness is made higher than that of another ink lower in lightness. For example, inks are prepared in such a manner that their penetrability becomes higher in the order of K < M = C < Y, thereby permitting speedy recording of clear and sharp images free from formation of inadequate feathering at boundaries between inks of different colors. <IMAGE>

Description

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an ink-jet recording method for conducting recording by using a plurality of inks to discharge the inks on a recording medium, and an apparatus for use in such a method.

Related Background Art

In recent years, apparatus for office automation such as computers, word processors and copying machines have widely spread. A great number of recording systems have hence been developed for use in recording apparatus thereof. Ink-jet recording apparatus have excellent features that they are easy to achieve high resolution and excellent in silence even at high speed compared with other recording systems, and moreover cheap. Needs for color recording are also increasing. Therefore, a great number of color ink-jet recording apparatus have also been developed. In the ink-jet recording apparatus, an ink is jetted from an nozzle to cause the ink to adhere on a recording paper sheet, thereby forming an image. The diameter of the nozzle is as small as about 50 to 100 µm. Therefore, inks for ink-jet recording are added with a non-volatile and high-hygroscopic solvent so as to prevent the inks from evaporating and drying to clog the nozzle at its tip. However, such inks have no quick drying property on recording media after recording though they have an effect to prevent the clogging due to the deposition of dye(s) in a nozzle orifice because they become hard to dry owing to the addition of a non-volatile wetting agent.
Color ink-jet recording apparatus involve a problem that color mixing (boundary feathering) occurs at boundaries between an ink of a certain color and other inks of different colors due to diffusion of dyes contained in the individual inks, resulting in deterioration in image quality. This color mixing is caused by mixing of an ink, which has been discharged on a paper sheet and exists on and in the paper sheet in a state that it is not sufficiently dried and fixed, with another ink of a different color, which adjoins the former ink. This mixing is caused by diffusion of coloring matter (colorants such as dyes and pigments) in a liquid-liquid interface between different inks. Therefore, the color mixing particularly tends to occur at such boundaries between different colors when ink-jet recording inks having no quick drying property are used.
In order to impart quick drying property to inks used in ink-jet recording systems, it has heretofore been attempted to add a surface active agent into an ink, thereby lowering the surface tension of the ink to increase its penetrating power into paper so as to penetrate into paper, or to add a solvent relatively high in vapor pressure into an ink, thereby lowering the surface tension of the ink to increase its penetrating power into paper and drying the ink owing to the evaporation of this solvent. Alternatively, it has been proposed to use only paper sheets high in permeability even in the case where inks to be used have no quick drying property or to decrease (or thin out) the amount of an ink to be jetted by one scan and then repeat the scan several times at proper intervals (multipass printing). Furthermore, it has also been attempted to provide a fixing device to forcedly evaporate inks.
When the surface active agent or the solvent high in vapor pressure is added too much, however, the wettability to paper becomes higher. Therefore, dots spread in a direction parallel to the paper surface and the dot diameter becomes greater correspondingly, whereby the sharpness of their edges is lost. Furthermore, the dot density is also lowered because the penetrating power of the ink is increased, whereby the ink permeates to a greater extent in a direction perpendicular to the paper surface. Besides, the excessive addition of the solvent high in vapor pressure facilitates the evaporation of the ink and hence involves a drawback that clogging tends to occur.
If paper sheets to be used are limited to special paper sheets for exclusive use, there are drawbacks that consumers can not use those other than these paper sheets and such paper sheet are very expensive.
In the case of the multipass printing, there is a problem that the number of times of scan increases and printing time per sheet (throughput) becomes very long if an interval of time in scan is lengthened.
The use of the fixing device involves a drawback that the apparatus is made a larger size as a whole and there is a poor economy from the viewpoint of energy.
As described above, various drawbacks are involved in imparting the quick drying property to inks used in the ink-jet recording apparatus. Therefore, these must be well balanced upon designing an ink-jet recording apparatus. In order to achieve reduction in size, cheap cost and speedy recording of images, however, there is at least a problem that when an ink of a certain color adjoins another ink of a different color before they are sufficiently dried and fixed on a paper sheet, unintended mixing of coloring matter (boundary feathering) as described above occurs at their contact boundaries, resulting in an irregular and blurred image.

SUMMARY OF THE INVENTION

The present invention provides an ink jet recording apparatus having the features set out in claim 1 of the accompanying claims.
The invention also provides an ink jet recording method having the features set out in claim 13 of the accompanying claims. Embodiments of the above mentioned method and apparatus permits speedy recording of bright and sharp images which are relatively free from feathering which would otherwise arise at boundaries between inks of different colours.
How the invention may be put into effect will now be described, by way of example only, with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic illustration of an ink-jet recording apparatus to which the present invention is applied;
Figs. 2A and 2B illustrate the boundary feathering of an image;
Fig. 3 illustrates an influence of a difference in lightness on vision in boundary feathering;
Fig. 4 illustrates a boundary region of an image when printed in accordance with the method of the present invention; and
Fig. 5 illustrates boundary feathering.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention will hereinafter be described by the following examples. However, these examples are intended to illustrate the invention more specifically and are not to be construed to limit the scope of the present invention.
Fig. 1 illustrates a schematic view of an ink-jet recording apparatus to which the present invention is applied. Herein, reference character C denotes an ink-jet cartridge provided with an ink tank at its upper part and a recording head at its lower part. In addition, the cartridge C is provided with a connector adapted to receive signals or the like for driving the recording head. Reference numeral 2 indicates a carriage on which four cartridges C₁, C₂, C₃ and C₄ (in which inks of different colors, for example, yellow, magenta, cyan, black, etc., have been separately contained) are mounted in predetermined positions and moreover, a connector holder adapted to transmit the signals or the like for driving the recording head is provided. The carriage 2 is designed so as to be electrically connected to the recording head. Reference numerals 11 and 52 denote a rail for scanning, which extends in a mainly scanning direction of the carriage 2 and slidably supports the carriage 2, and a drive belt adapted to transmit drive power for reciprocally driving the carriage 2, respectively. Reference numerals 15, 16 and 17, 18 indicate pairs of feed rollers, which have been respectively arranged before and behind a recording position by the recording head, and feed a recording medium with it held therebetween. Reference character P designates a recording medium such as paper, which is brought into contact under pressure with a platen (not illustrated) for regulating the recording surface of the recording medium P flat. At this time, the recording head of the ink-jet cartridge C mounted on the carriage 2 projects downward from the carriage 2 and is positioned between the rollers 16 and 18 for feeding the recording medium P, and the discharging orifice-defining surface of the recording head is positioned so as to be opposed in parallel to the recording medium P brought into contact under pressure with the guide face of the platen (not illustrated).
In the ink-jet recording apparatus of this embodiment, a recovery system unit 200 is arranged on the home position side situated on the left of the drawing. In the recovery system unit, reference numeral 300 designates a cap unit provided correspondingly to each of the plural ink-jet cartridges C. The cap unit 300 is slidable in left and right directions viewed from the drawing as the carriage 2 is moved and moreover, vertically movable. The cap unit 300 comes into contact with the recording head to cap it when the carriage is situated at the home position, thereby preventing the ink within a discharging orifice of the recording head from evaporating to increase the viscosity of the ink and fix to the orifice and hence resulting in discharge failure.
In the recovery system unit 200, reference numeral 500 indicates a pump unit communicating with the cap unit 300 and adapted to generate a negative pressure to be used in a recovery treatment by suction, which is conducted by bring the cap unit 300 into contact with the recording unit, or the like if the recording head should become discharge failure. In the recovery system unit, further, reference numeral 401 designates a blade formed with an elastic material such as rubber and serving as a wiping member. Reference numeral 402 indicates a blade holder for holding the blade 401.
In this apparatus, black, cyan, magenta and yellow inks are respectively contained in the four ink-jet cartridges C₁, C₂, C₃ and C₄ mounted on the carriage 2 to use them. In this order, these inks are overlaid to each other by reciprocally moving the carriage 2 along the rail for scanning 11. Colors between primary colors can be realized by suitably overlaying ink dots of cyan, magenta and yellow to each other. Namely, red, blue and green can be realized by overlaying magenta to yellow, cyan to magenta, and cyan to yellow, respectively.
In general, black can be realized by overlapping three colors of cyan, magenta and yellow to each other. However, the color development of black at this time is poor, and the jetted amount of the inks per unit area becomes larger. Therefore, it is generally carried out to independently jet only a black color.
First of all, color printing was conducted with four inks of cyan, magenta, yellow and black colors, which have each the following Composition 1:

Composition 1:

Dye	2.5 % by weight
Triethylene glycol	10.0 % by weight
Glycerol	10.0 % by weight
Ethyl alcohol	5.0 % by weight
Distilled water	72.5 % by weight

At this time, as illustrated in Fig. 5, unintended color mixing occurs at a boundary (on a line connecting points A and A′ in the drawing) in which a solid printed area of a certain color adjoins a solid printed area of another color. Furthermore, at this time, feathering occurs along uneven irregularities and fibers on the paper surface. Therefore, this feathering does not become linearly smooth, but becomes extremely conspicuous, resulting in an image lacking in sharpness. This phenomenon is assumed to be caused by a mechanism illustrated in Figs. 2A and 2B. Namely, the absorption of ink into paper is believed to be advanced in the order of contact, impingement, dot-formation, penetration and drying (fixing) as illustrated in Fig. 2A. When an ink of a certain color adjoins another ink of a different color at a stage from the dot-formation to the penetration as illustrated in Fig. 2B, the diffusion of ink occurs there. When the degree of this diffusion is great, feathering occurs at the boundary.
The boundary feathering between different colors is apt to be conspicuous at the boundaries between a yellow color and other colors. This is believed to be attributed to visual effect by which the feathering looks to occur from the side lower in lightness to the side higher in lightness at boundaries between colors greatly different in lightness from each other. Fig. 3 schematically illustrates this fact. Near the boundary between yellow and blue colors, a dark feathering region in which yellow, magenta and cyan are mixed with each other appears. At this time, the difference in lightness between the color of the dark feathering region and the blue color is small. Therefore, feathering therebetween is hard to be conspicuous. However, the difference in lightness between the yellow color and the color of the dark feathering region is great. Therefore, it is clearly recognized that feathering occurs therebetween. Accordingly, it is believed that the feathering looks to just occur from the side of the blue color lower in lightness to the side of the yellow color higher in lightness.

Example 1

In this invention, accordingly, an attempt to increase the penetrability of an ink high in lightness was made by changing the amount of the solvent high in vapor pressure and/or the like to be added as described above to adjust the penetrability of the ink. First of all, the penetrability of an ink having the following Composition 2 was compared with that of an ink having Composition 1 as described above in accordance with the Bristow method. As a result, it was found that the ink of Composition 2 is higher in penetrability than the ink of Composition 1.

Composition 2:

Dye	2.5 % by weight
Triethylene glycol	10.0 % by weight
Glycerol	10.0 % by weight
Ethyl alcohol	7.0 % by weight
Distilled water	70.5 % by weight

Color printing was conducted by changing the composition of the yellow ink to Composition 2 while the compositions of the black, cyan and magenta inks remained Composition 1. As a result, feathering at boundaries between the yellow color and the other colors, which was apt to be particularly conspicuous, became almost inconspicuous, thereby permitting clear recording. Fig. 4 schematically illustrates this fact. This is believed to be attributed to the fact that since the force of the yellow ink, which will flow into the cyan and magenta inks, is stronger than the force of the cyan and magenta inks, which will flow into the yellow ink, the inks other than the yellow ink become difficult to penetrate into the region of a yellow image beyond the boundary.
In this example, an alcohol high in vapor pressure was used to adjust the penetrability of the inks. However, no particular limitation is imposed on such an agent. Surface active agents or other solvents may also be used.
In the following inks, isopropyl alcohol and acetylenol as a surface active agent were used to adjust the penetrability of the inks. The penetrability of a yellow ink was made higher than that of other inks like the aforesaid example.

Black ink:

Dye	3.0 % by weight
1,2,6-Hexanetriol	7.0 % by weight
Triethylene glycol	7.0 % by weight
Isopropyl alcohol	1.5 % by weight
Acetylenol	0.01 % by weight
Lithium acetate	0.02 % by weight
Distilled water	81.47 % by weight

Cyan ink:

Dye	2.5 % by weight
1,2,6-Hexanetriol	7.0 % by weight
Triethylene glycol	7.0 % by weight
Isopropyl alcohol	1.5 % by weight
Acetylenol	0.01 % by weight
Lithium acetate	0.05 % by weight
Distilled water	81.94 % by weight

Magenta ink:

Dye	2.5 % by weight
1,2,6-Hexanetriol	7.0 % by weight
Triethylene glycol	7.0 % by weight
Isopropyl alcohol	1.5 % by weight
Acetylenol	0.01 % by weight
Distilled water	81.99 % by weight

Yellow ink:

Dye	1.5 % by weight
1,2,6-Hexanetriol	7.0 % by weight
Triethylene glycol	7.0 % by weight
Isopropyl alcohol	2.5 % by weight
Acetylenol	0.02 % by weight
Lithium acetate	0.05 % by weight
Distilled water	81.93 % by weight

With respect to the dye used as a colorant in each ink, any dyes may be used so long as they are free from any changes of tone and formation of any precipitate. pigments may also be used.

Example 2

In this example, four inks of black (K), cyan (C), magenta (M) and yellow (Y), which were used in an ink-jet recording apparatus in which the inks were jetted in the order of K, C, M and Y, were prepared in such a manner that the penetrability of the four inks into paper became higher in jetting order. In the case of ink-jet recording, an ink to be jetted subsequently tends to be attracted by another ink jetted previously to cause feathering as illustrated in Fig. 2B.
Accordingly, with respect to the jetting order of the inks, it may safely be said that it is preferred to jet an ink higher in lightness later. In this example, taking into account these facts, printing is fixed to one way and the cyan and magenta inks, the yellow ink, and the black ink were prepared in accordance with Composition 1, Composition 2 and the following Composition 3, respectively, so that the penetrability of the respective inks may satisfy the following relationship: $K < C = M < Y$

Composition 3:

Dye	2.5 % by weight
Triethylene glycol	10.0 % by weight
Glycerol	10.0 % by weight
Ethyl alcohol	3.0 % by weight
Distilled water	74.5 % by weight

Since the lightnesses of the cyan and magenta inks are almost equal to each other, their penetrating rates were made even. By preparing the inks in this manner, not only feathering at boundaries between the yellow color and the other colors, which was apt to be particularly conspicuous, but also feathering at boundaries of other combinations became inconspicuous, thereby permitting recording of clear and sharp color images.

Example 3

Among ink-jet recording apparatus, there are also those in which inks were jetted in the order of C, M, Y and K. In the case of ink-jet recording, as has been described above, an ink to be jetted subsequently tends to be attracted by another ink jetted previously to cause feathering as illustrated in Fig. 2B. Accordingly, with respect to the jetting order of the inks, it is preferred to jet an ink lower in lightness earlier. In the ink-jet recording apparatus, there is a problem that fog-like minute ink droplets called mist are generated upon jetting of an ink, and these droplets adhere to the succeeding recording heads, resulting in image inferiority. The black ink particular tends to smear other inks. Therefore, the black ink is jetted last.
In this example, the black ink lowest in lightness comes to be jetted last. In the case of ink-jet recording, an ink to be jetted subsequently tends to be attracted by another ink jetted previously to cause feathering as illustrated in Fig. 2B. In this case, the black ink lowest in lightness is in a state apt to feather still more. Accordingly, it is more preferable to make the difference in penetrating rate between the black ink and the other inks still greater as shown below. $K << C = M < Y$
The compositions of the inks of different colors in this example are shown below.

Black ink:

Cyan ink and magenta ink:

Dye	2.5 % by weight
Triethylene glycol	10.0 % by weight
Glycerol	10.0 % by weight
Ethyl alcohol	5.0 % by weight
Acethylenol	0.5 % by weight
Distilled water	72.0 % by weight

Yellow ink:

Dye	2.5 % by weight
Triethylene glycol	10.0 % by weight
Glycerol	10.0 % by weight
Ethyl alcohol	7.0 % by weight
Acethylenol	0.5 % by weight
Distilled water	70.0 % by weight

Example 4

When the ink-jet recording apparatus is of a both-way printing type, inks are jetted in the order of K, C, M, Y in the forward direction (upon the forward movement of the carriage 2) and in the order of Y, M, C and K in the backward direction (upon the backward movement of the carriage 2).
In the case of ink-jet recording, an ink to be jetted subsequently tends to be attracted by another ink jetted previously to cause feathering as illustrated in Fig. 2B. Therefore, the ink lower in lightness is in a state apt to feather in the direction higher in lightness in the case of the printing in the backward direction because such an ink is jetted later. Accordingly, it is more preferable to make the difference in penetrating rate between the black ink and the other inks still greater than that in the one-way printing as shown below. $K << C = M << Y$

Black ink:

Cyan ink and magenta ink:

Dye	2.5 % by weight
Triethylene glycol	10.0 % by weight
Glycerol	10.0 % by weight
Isopropyl alcohol	3.0 % by weight
Distilled water	74.5 % by weight

Yellow ink:

Dye	2.5 % by weight
Triethylene glycol	10.0 % by weight
Glycerol	10.0 % by weight
2-Butyl alcohol	3.0 % by weight
Distilled water	74.5 % by weight

Since the lightnesses of the cyan and magenta inks are almost equal to each other, their penetrating rates were made even. By preparing the inks in this manner, even when conducting both-way printing, not only feathering at boundaries between the yellow color and the other colors, which was apt to be particularly conspicuous, but also feathering at boundaries of other combinations became inconspicuous, thereby permitting recording of bright and sharp color images.

Example 5

The lightness of an ink may vary depending on the concentration of a dye contained in the ink and a recording medium to be used. Therefore, the lightness of a magenta ink may be higher than that of a cyan ink in same cases. In this case, the lightnesses of the inks become higher in the order of K, M, C and Y. In such a case, it is preferred to prepare the inks in such a manner that their penetrability becomes higher in the following order: $K << M < C << Y$

Black ink:

Cyan ink:

Magenta ink:

Dye	2.5 % by weight
Triethylene glycol	10.0 % by weight
Glycerol	10.0 % by weight
Isopropyl alcohol	3.0 % by weight
Acethylenol	0.5 % by weight
Distilled water	74.0 % by weight

Yellow ink:

Dye	2.5 % by weight
Triethylene glycol	10.0 % by weight
Glycerol	10.0 % by weight
2-Butyl alcohol	3.0 % by weight
Acethylenol	0.5 % by weight
Distilled water	74.0 % by weight

In this example, not only feathering at boundaries between the yellow color and the other colors, which was apt to be particularly conspicuous, but also feathering at boundaries of other combinations also became inconspicuous like the above-described examples, thereby permitting recording of clear and sharp color images.
In the above examples, the respective color inkε were prepared by thoroughly mixing and dissolving the whole components mentioned above for each ink in a container and thereafter, filtrating the resulting mixture under pressure through a Teflon (trade name) filter having a pore size of 1 µm.
The present invention can still more exhibit its effects when combined with a method in which the amount of an ink to be jetted by one scan is decreased (or thinned out) and the scan is then repeated several times at proper intervals (multipass printing), or the use of a fixing device to forcedly evaporate inks. At this time, the incorporation of the present invention permits the shortening of number of times of scan and interval of time in scan to a considerable extent and moreover the exhibition of sufficient effects even when a fixing device small in size and low in consumption power is used.
In these examples, excellent effects can be obtained particularly in a recording head and a recording apparatus of a system in which a means (for example, an electro-thermal converting element, laser beam, etc.) for generating thermal energy as energy used in discharging an ink is equipped, and the change of state of the ink is caused to take place by the thermal energy, among the ink-jet recording systems. According to such a system, recording high in density and resolution can be achieved.
With respect to its typical structure and principle, it is preferred to employ the basic principle disclosed in, for example, U.S. Patent Nos. 4,723,129 and 4,740,796. This system can be applied to both so-called "On-Demand" type and "Continuous" type structures. This system is advantageous to the On-Demand type in particular because an electro-thermal converting element disposed to align to a sheet or a liquid passage in which a liquid (ink) is held is applied with at least one drive signal which corresponds to information to be recorded and which enables the temperature of the electro-thermal converting element to be rapidly raised higher than a nuclear boiling point, so that thermal energy is generated in the electro-thermal converting element and film boiling is caused to take place on the surface of the recording head which is heated. As a result, bubbles can be respectively formed in the liquid (ink) in response to the drive signals. Owing to the enlargement and contraction of the bubbles, the liquid (ink) is discharged through the discharging orifice, so that at least one droplet is formed. In a case where the aforesaid drive signal is made to be a pulse signal, a further satisfactory effect can be obtained in that the bubbles can immediately and properly be enlarged/contracted and the liquid (ink) can be discharged while exhibiting excellent responsibility. It is preferable to use a drive signal of the pulse signal type disclosed in U.S. Patent Nos 4,463,359 and 4,345,262. Furthermore, in a case where conditions for determining the temperature rise ratio on the aforesaid heating surface disclosed in U.S. Patent No. 4,313,124 are adopted, a further excellent recording operation can be performed.
In addition to the structure (a linear liquid passage or a perpendicular liquid passage) of the recording head formed by combining the discharging orifice, the liquid passage and the electro-thermal converting element as disclosed in the aforesaid specifications, a structure disclosed in U.S. Patent Nos. 4,558,333 and 4,459,600 in which the heated portion is disposed in a bent portion is included in the scope of the present invention. Furthermore, the present invention can effectively be embodied in a structure in which a common slit is made to be the discharge portion of a plurality of electro-thermal converting elements and which is disclosed in Japanese Patent Application Laid-Open No. 59-123670 and a structure in which an opening for absorbing thermal energy pressure wave is defined to align to the discharge part and which is disclosed in Japanese Patent Application Laid-Open No. 59-138461. Namely, according to the present invention, recording operation can be performed surely and effectively irrespective of the form of the recording head.
The present invention may be applied to a full line type recording head having a length which corresponds to the maximum width of the recording medium, which can be recorded by the recording apparatus. Such a recording head may be either a structure capable of realizing the aforesaid length and formed by combining a plurality of recording heads or a structure formed by an integrally formed recording head.
In addition, the present invention can also be effectively applied to a recording head fixed to the body of the apparatus, a structure having an interchangeable chip type recording head which can be electrically connected to the body of the apparatus or to which an ink can be supplied from the body of the apparatus when it is mounted on the body of the apparatus, or a cartridge type recording head provided with an ink tank integrally formed to the recording head itself among the above-exemplified serial type recording heads.
It is preferable to additionally provide a recording head recovery means and an auxiliary means of the recording apparatus according to the present invention because the effects of the present invention can further be stabled. Specifically, an effect can be obtained in that the recording operation can be stably performed by providing a recording head capping means, a cleaning means, a pressurizing or sucking means, an electro-thermal converting element or another heating device or an auxiliary heating means formed by combining the aforesaid elements and by performing a previous discharge mode in which a discharge is performed individually from the recording operation.
Although the embodiments of this invention, which have been described above, used the liquid inks, inks which are solid at a temperature lower than room temperature, but are softened or liquefied at room temperature may be used. In the aforesaid ink-jet system, the temperature of an ink is usually controlled in a range from 30°C to 70°C so as to adjust the viscosity of the ink within a stable discharge range. Therefore, it is only necessary to use inks which is liquefied in response to a record signal applied. Furthermore, inks the temperature rise of which is prevented by positively using the temperature rise due to the thermal energy as energy of state change from the solid state to the liquid state of ink or inks which are solidified when it is allowed to stand in order to prevent the evaporation of ink may be used. That is, inks which are liquefied by thermal energy for the first time such as inks liquefied by thermal energy applied in response to the record signal and discharged as ink droplets or inks which already begin to solidify when they reach the recording medium may be employed in the present invention. In this case, an ink may be, in the form of liquid or solid, held by a recess of a porous sheet or a through hole as disclosed in Japanese Patent Application Laid-Open No. 54-56847 or 60-71260 and disposed to confront the electro-thermal converting element. It is most preferable for the above-described inks that an ink be discharged by the aforesaid film boiling method.
Furthermore, the ink-jet recording apparatus according to this invention may be in the form, in addition to that used as an image-output terminal for information processing equipment such as a computer, of a copying machine combined with a reader and moreover, of a facsimile terminal equipment having a transmit-receive function or the like.
As has been described above, the present invention can provide ink-jet recording apparatus, which are cheap and small in size and permit speedy recording of clear and sharp images free from formation of inadequate feathering at boundaries between inks of different colors, without making any changes in construction of existent apparatuses.

Claims

An ink jet recording apparatus comprising first, second and third recording means containing and adapted to discharge respective first, second and third inks onto a paper recording medium, the second ink being lighter in colour than the first ink and the third ink being lighter in colour than the second ink, and transfer means for bringing about relative movement between the recording medium and the first, second and third recording means, characterised in that the third ink has a greater penetrability into the recording medium than the first and second inks.
The apparatus of claim 1, wherein the penetrability of the second ink into the recording medium is greater than that of the first ink and less than that of the third ink.
The apparatus of claim 1, wherein the penetrability of the first ink into the recording medium is the same as that of the second ink.
The apparatus of any of claims 1 to 3, wherein the first, second and third recording means are arranged on the transfer means in such a manner that the first and second inks arrive at the recording medium earlier than the third ink.
The apparatus of any of claims 1 to 4, wherein the third ink is a yellow ink.
The apparatus of any preceding claim, wherein the first ink is a cyan ink.
The apparatus of any of claims 1 to 6, wherein the second ink is a magenta ink.
The ink jet recording apparatus of any preceding claim, further comprising a fourth recording means for discharging a fourth ink onto the recording medium, the fourth ink being darker in colour than the first ink.
The apparatus of claim 8, wherein the fourth ink is a black ink.
The apparatus of any preceding claim, wherein each of the recording means comprises a plurality of recording elements for discharging ink droplets.
The apparatus of claim 10, wherein the recording means uses thermal energy to bring about a change of state of the ink and thereby discharge ink droplets through a discharge opening.
The apparatus of any of claims 1-11 further comprising the paper recording medium.
An ink jet recording method which comprises using a first, second and third recording means to discharge respectively a first, second and third ink whose colours differ from one another in lightness to record an image on a paper recording medium by deposition of the first, second and third inks thereon, wherein the third ink is lighter in colour than the first and second inks, characterised in that the penetrability of the third ink into the recording medium is greater than those of the first and second inks.
The method of claim 13, wherein the penetrability of the second ink into the recording medium is greater than that of the first ink and less than that of the third ink.
The method of claim 13, wherein the penetrability of the first ink into the recording medium is the same as that of the second ink.
The method of any of claims 13 to 15, wherein the first, second and third recording means are arranged on the transfer means so that the first and second inks arrive at the recording medium earlier than the third ink.
The method of any of claims 13 to 16, wherein the third ink is a yellow ink.
The method of any of claims 13 to 17, wherein the first ink is a cyan ink.
The method of any of claims 13 to 18, wherein the second ink is a magenta ink.
The method of any of claims 13 to 19, further comprising a fourth recording means for discharging a fourth ink onto the recording medium, the fourth ink being darker in colour than the first ink.
The method of claim 20, wherein the fourth ink is a black ink.
The method of any of claims 13 to 21, wherein each of the recording means comprises a plurality of the recording elements for discharing an ink droplet.
The method of claim 22, wherein the recording means employs thermal energy to bring about change of state of the ink so as to cause discharge of ink droplets through a discharge opening.